In the stereo slide film on which an image is photographed by a stereoscopic camera of a structure having a fixed spacing between the optical axes of left and right lenses, non-superposed portions are left in the left edge portion of the left image plane and in the right edge portion of the right image plane in accordance with the subject distance by the difference in the field of view between the left and right photographic lenses.
For an observation with a stereo slide viewer, those non-superposed portions obstruct the view because of lack of the stereoscopic image. In order to eliminate this obstruction, there has been generally used a method of masking the non-superposed portions of the left and right image planes by making the image plane aperture width of the stereo slide mount narrower than the one image plane width of the stereo slide film.
The width of the non-superposed portions to be masked becomes the larger as the distance of the object, that will exert the most serious influence (although different according to the size, position, color, contrast and so on) upon the matching of the left and right images becomes shorter. Thus, the film is mounted by selecting the stereo slide mount having a proper image plane masking extent for each stereo slide film from a plurality of kinds of stereo slide mounts having aperture widths changed stepwise. Therefore, the film, on which an image has been photographed by an optical axis spacing fixed type stereoscopic camera, cannot avoid the loss in the image plane as a result of masking the image plane, and involves a defect that the loss in the image plane is increased at the time of a close shot.
On the other hand, the stereoscopic camera, which is equipped with a mechanism for adjusting the spacing between the optical axes of the left and right lenses, can adjust the fields of view of the left and right lenses so that it can correct the parallax according to the subject distance. It is, therefore, theoretically unnecessary to mask the outer edge portions of the left and right image planes with the slide mounts, so that a proper stereoscopic effect can be achieved if the films are uniformly mounted on the stereo slide mount having an aperture width equal to the image plane width of the films. However, even the film, on which an image has been photographed by the stereoscopic camera of the automatic optical axis spacing adjusting type or the manual optical axis spacing adjusting type, may be required to correct the perspective by masking the left and right image planes, as in the following case.
When an object having a serious influence upon the matching of the left and right images is photographed at a shorter distance than a main object, for example, the outer edge portions of the left and right image planes have to be masked to correct the perspective.
When the photograph is taken in the state of excess correction of parallax (for an excessively short optical axis spacing) by mistaking the adjustment of the optical axis spacing in the manual type optical axis spacing adjusting type stereoscopic camera, the perspective has to be corrected, contrary to the aforementioned case, by masking the inner edge portions of the left and right image planes.
However, the stereo slide film, on which an image has been photographed by the optical axis spacing adjusting type stereoscopic camera, is required to have an extremely small masking extent because the photograph is made in the state of the parallax corrected to some extent. Therefore, the suitable method is to mask a portion of the image plane by adjusting the offsets of the film for the apertures with the stereo slide mount which has a slightly smaller aperture width than the image plane width of the film.
In the stereo slide mount of the prior art, however, the film is positioned by bonding it to the base frame when the position of the film is adjusted with respect to the apertures of the mount. As a result, the positioning operation is difficult and provides no accuracy and is troublesome and inefficient.
Therefore, the invention has an object to solve the technical problem to be solved for providing a stereo slide mount which is both easy for the mounting operation and precise in the positioning operation.